Spark from the Deep tells the story of how human beings came to understand and use electricity by studying the evolved mechanisms of strongly electric fish. These animals have the ability to shock potential prey or would-be predators with high-powered electrical discharges. The author asks completely fresh questions about the evolutionary, environmental, and historical aspects of people's interest in electric fish. Stimulated by painful encounters with electric catfish, torpedos, and electric eels, people learned to harness the power of electric shock for medical therapies and eventually developed technologies to store, transmit, and control electricity. Now we look to these fish as an inspiration for engineering new sensors, computer interfaces, autonomous undersea robots, and energy-efficient batteries.